Along with rapid progress in information communication appliances such as mobile telephone, PHS (personal handy-phone system), and PDA (personal digital assistants), the infrastructure capable of accessing and transmitting easily anytime, anywhere, by anyone is being prepared. They are intended for mobile applications, and the display unit of light weight, thin structure, and low power consumption is required, and the liquid crystal display device is presently in the mainstream. The liquid crystal display device is designed to display by varying the light transmission intensity by driving liquid crystal molecules at an effective voltage of several volts, but the liquid crystal itself is a non-luminous substance, and some other light source is needed. The light source requires a very large power supply as compared with the power for driving the liquid crystal, but a reflective liquid crystal display device for displaying by utilizing the surrounding light by disposing a reflector at the lower side of the liquid crystal display device can realize a display device making use of the intrinsic feature of extremely low power consumption of the liquid crystal. The reflective liquid crystal display device comes to be indispensable as one of displays for mobile information terminals.
In the reflective liquid crystal display device, however, since the surrounding light is utilized for display, the brightness can be obtained only in the specular reflection direction of incident light to the display device. Accordingly, to extend the angle of the viewing field, it is proposed to use a scattering film for scattering the light into other regions than the specular reflection direction.
Conventional reflective liquid crystal display devices include, among others, the one using a front scattering film as disclosed in Japanese Laid-open Patent No. 8-201802 (hereinafter called prior art I), and the one having scattering characteristics by undulations formed on an upper substrate or the like as disclosed in Japanese Laid-open Patent No. 8-338993 (hereinafter called prior art II).
However, if provided with scattering characteristics by undulations as in prior art II, back scattering occurs at the time of incidence of surrounding light into the liquid crystal display device. As a result, the reflectivity in black display is not lowered sufficiently, and high contrast is not obtained.
FIG. 13 shows a structure of the reflective liquid crystal display device of prior art I, in which reference numeral 80 is a front scattering film, 81 is a polarizer, 82 is a retardation film, 83 is a liquid crystal cell, 84 is a transparent substrate, 85 is a color filter, 86 is a transparent electrode, 87 is a liquid crystal layer, 88 is a mirror reflector, and 89 is a lower substrate.
Even in such constitution using the front scattering film as in prior art I, since the scattering angle region is omnidirectional, due to scattering of light by scattering film, the light is diffused also in the direction not visible from the viewer out of the exit light from the liquid crystal display device. Accordingly, the exit light is not utilized effectively, and sufficient brightness is not obtained in white display in the viewer's observing direction, and the contrast is lowered. Usually, the main observing direction of the viewer is the normal direction of the liquid crystal display device, but the light is diffused in this direction when emitted from the scattering film, and the image appears to be blurry.